The invention relates to a process for the preparation of an aromatic hydrocarbon mixture from a mixture of carbon monoxide and hydrogen using a mixture of two catalysts of which one has the capability of catalyzing the conversion of an H.sub.2 /CO mixture into acyclic oxygen-containing hydrocarbons, and the other is a crystalline silicate having the capability of catalyzing the conversion of acyclic oxygen-containing hydrocarbons into aromatic hydrocarbons. The crystalline silicates employed in the process to the invention are characterized in that they have the following properties:
(a) thermally stable up to a temperature above 600.degree. C., PA0 (b) an X-ray powder diffraction pattern showing, inter alia, the reflections given in Table A. PA0 wherein the letters used have the following meanings: PA0 VS=very strong; S=strong; M=moderate; W=weak; .theta.=angle according to Bragg. PA0 (c) in the formula which gives the composition of the silicate, expressed in moles of the oxides, and in which, in addition to oxides of hydrogen, alkali metal and/or alkaline-earth metal and silicon, an oxide of a trivalent metal A are present, the A.sub.2 O.sub.3 /SiO.sub.2 molar ratio (for the sake of brevity further designated m in this patent application) is less than 0.1. PA0 (a) thermally stable up to a temperature above 600.degree. C., PA0 (b) an X-ray powder diffraction pattern showing, inter alia, the reflections given in Table A of the specification, PA0 (c) in the formula which gives the composition of the silicate, expressed in moles of the oxides, and in which, in addition to oxides of hydrogen, alkali metal and/or alkaline-earth metal and silicon, gallium oxide is present, the Ga.sub.2 O.sub.3 /SiO.sub.2 molar ratio (m) is less than 0.1, to produce a contact product, and separating an aromatic hydrocarbon mixture from said contact product.
TABLE A ______________________________________ Radiation: Cu - K Wavelength 0.15418 nm 2 .theta. relative intensity ______________________________________ 7.8-8.2 S 8.7-9.1 M 11.8-12.1 W 12.4-12.7 W 14.6-14.9 W 15.4-15.7 W 15.8-16.1 W 17.6-17.9 W 19.2-19.5 W 20.2-20.6 W 20.7-21.1 W 23.1-23.4 VS 23.8-24.1 VS 24.2-24.8 S 29.7-30.1 M ______________________________________
In an investigation by the Applicants concerning the above-mentioned process using the catalyst mixtures in which as the crystalline silicate component an aluminum silicate has been employed, it has been found that the activity and selectivity of these catalyst mixtures are greatly dependent on m of the aluminum silicate. It has been found that catalyst mixtures in which an aluminum silicate with a low value for m is present, show a high selectivity and a low activity, whereas catalyst mixtures in which an aluminum silicate with a high value for m is present, show exactly the opposite behavior. For application of the process on a technical scale a catalyst mixture is needed which has both a high activity and a high selectivity.
Further investigation by the Applicants concerning the above-mentioned process has shown that this requirement can be met by using a crystalline silicate which has the properties mentioned under (a)-(c) and which contains as the trivalent metal gallium. For, with catalyst mixtures in which the crystalline aluminum silicate has been replaced by a crystalline gallium silicate, the catalytic behavior in the above-mentioned process has been found to be independent of m of the gallium silicate. Both with gallium silicates with a low value for m and with gallium silicates with a high value for m catalyst mixtures can be prepared which show, when using the above mentioned process, the high selectivity of a catalyst mixture which contains an aluminum silicate with a low value for m and, at the same time, the high activity of a catalyst mixture which contains an aluminum silicate with a high value for m.